TW201505355A - Rotational speed control device, method and system of motor - Google Patents

Abstract

The disclosure relates to a rotational speed control device of a motor. The rotational speed control device includes a reference voltage generating module for generating a reference voltage, a PWM signal converting module for converting a PWM signal into a voltage signal corresponding to the duty ratio of the PWM signal, a first comparator for outputting a first level if the voltage of the voltage signal is less than the voltage of the reference voltage and outputting a second level if the voltage of the voltage signal is greater than the voltage of the reference voltage, a first switch having a control terminal connected with a output terminal of the first comparator, which is turned on for inputting a first signal when receiving the second level and turned off when receiving the first level, a follower having a input terminal connected with the PWM signal converting module, and a control signal output terminal for outputting the first signal received by the first switch or the voltage signal received by the follower and converted from the PWM signal to a motor control circuit.

Description

Motor speed control device, method and system

The present application relates to motor control technology, and more particularly to a motor speed control device, method and system.

Figures 1 through 4 are four motor speed control curves showing the relationship between the motor speed control signal and the motor speed. The motor speed control signal may be a current signal, a voltage signal, or an electrical signal such as a Pulse Width Modulation (PWM) signal having a duty cycle. In these four figures, the abscissa indicates the duty ratio of the PWM signal used to control the motor speed, and the ordinate indicates the motor speed.

Comparing Fig. 1, Fig. 2 with Fig. 3 and Fig. 4, it can be found that in Fig. 3 and Fig. 4, the motor speed can be changed from low speed or static to higher speed under a certain duty ratio, as shown in the figure. As shown in Fig. 3, when the duty ratio is about 30%, the motor speed is sharply increased from about 800 RPM (Revolutions Per Minute, RPM) to about 1600 RPM, as shown in Fig. 4, when the duty ratio is about 30%, the motor The rotational speed increased sharply from 0 RPM to approximately 1600 RPM; however, the motor speeds in Figures 1 and 2 did not have such a jump.

In some applications, it is desirable to use the motor speed control curves shown in Figures 3 and 4. For example, in a fan of a home appliance and a fan of a Central Process Unit (CPU), it is desirable that the rotational speed of the motor can jump at a certain duty ratio.

However, in the prior art, only the control curves shown in FIGS. 1 and 2 can be realized at present, and the control curves shown in FIGS. 3 and 4 cannot be realized.

In order to solve the above problems, the present application provides a motor speed control device, method and system, which enable a motor to be rapidly changed from a low speed or a stationary state to a higher speed at a certain duty ratio, that is, as shown in FIGS. 3 and 4 The control curve shown.

The application provides a motor speed control device, including:

a reference voltage generating module for generating a reference voltage;

a PWM signal conversion module, configured to convert the PWM signal into a voltage signal, where the voltage signal corresponds to a duty ratio of the PWM signal;

a first comparator, the positive end of which is connected to the reference voltage generating module, and the negative end thereof is connected to the PWM signal conversion module, and is configured to output when the voltage of the voltage signal converted by the PWM signal is less than or equal to the reference voltage a level, when the voltage of the voltage signal converted by the PWM signal is greater than the reference voltage, outputting a second level;

a first switching element, the control end of which is connected to the output end of the first comparator, and the first end thereof inputs a first signal for conducting when receiving the second level outputted by the output end of the first comparator, Connecting the first end of the first switching element to the second end, and cutting off when receiving the first level outputted by the output end;

a follower whose input terminal is connected to the PWM signal conversion module;

Control signal output terminals respectively connected to the second end of the first switching element and the output of the follower for receiving the first signal through the second end of the first switching element or through the follower The voltage signal converted by the received PWM signal is output to the motor control circuit;

Wherein, when the first switching element is turned on, the motor control circuit inputs the first signal, the first signal causes the motor control circuit to control the motor speed to be 0 or a determined speed; when the first switching element is turned off, The motor control circuit inputs a voltage signal converted by the PWM signal such that the motor speed is determined by a duty cycle of the PWM signal.

The present application also provides a motor speed control method implemented by the foregoing motor conversion device, including:

Converting the PWM signal into a voltage signal by the PWM signal conversion module, and comparing the voltage of the converted PWM voltage signal with a reference voltage through the first comparator;

If the voltage of the voltage signal converted by the PWM signal is greater than the reference voltage, outputting the second level through the first comparator, so that the first switching element is turned on to the first end and the second end of the first switching element End communication, transmitting the first signal received by the first end of the first switching element to the motor control circuit, such that the motor control circuit controls the motor speed to be 0 or a determined speed;

If the voltage of the voltage signal converted by the PWM signal is less than or equal to the reference voltage, the first level is outputted by the first comparator, so that the first switching element is turned off, and the voltage converted by the PWM signal conversion module is converted by the follower. The signal is provided to the motor control circuit such that the motor speed is determined by the duty cycle of the PWM signal.

The embodiment of the present application further provides a motor speed control system, including:

motor;

a motor control circuit coupled to the motor for controlling a rotational speed of the motor;

a motor speed control device connected to the motor control circuit;

The motor speed control device includes:

a reference voltage generating module for generating a reference voltage;

a PWM signal conversion module, configured to convert the PWM signal into a voltage signal, where the voltage signal corresponds to a duty ratio of the PWM signal;

a first comparator, the positive end of which is connected to the reference voltage generating module, and the negative end thereof is connected to the PWM signal conversion module, and is configured to output when the voltage of the voltage signal converted by the PWM signal is less than or equal to the reference voltage a level, when the voltage of the voltage signal converted by the PWM signal is greater than the reference voltage, outputting a second level;

a first switching element, the control end of which is connected to the output end of the first comparator, and the first end thereof inputs a first signal for conducting when receiving the second level outputted by the output end of the first comparator, Connecting the first end of the first switching element to the second end, and cutting off when receiving the first level outputted by the output end;

a follower whose input terminal is connected to the PWM signal conversion module;

Control signal output terminals respectively connected to the second end of the first switching element and the output of the follower for receiving the first signal through the second end of the first switching element or through the follower The voltage signal converted by the received PWM signal is output to the motor control circuit;

Wherein, when the first switching element is turned on, the motor control circuit inputs the first signal, the first signal causes the motor control circuit to control the motor speed to be 0 or a determined speed; when the first switching element is turned off, The motor control circuit inputs a voltage signal converted by the PWM signal such that the motor speed is determined by a duty cycle of the PWM signal.

In the embodiment of the present application, it can be seen that when the voltage of the voltage signal converted into the PWM signal is less than or equal to the reference voltage, that is, the duty ratio of the PWM signal is greater than or equal to the duty ratio corresponding to the reference voltage, A first level of a comparator output causes the first switching element to be turned off, thereby inputting a voltage signal into which the PWM signal is converted to the motor control circuit, such that the motor control circuit controls the motor speed to vary as the duty cycle of the PWM signal changes. When the voltage of the voltage signal converted into the PWM signal is greater than the reference voltage, that is, the duty ratio of the PWM signal is less than the duty ratio corresponding to the reference voltage, the second level of the first comparator output causes the first switching element to be turned on The first signal is thereby input to the motor control circuit such that the motor control circuit controls the motor speed to be zero or a determined speed (eg, approximately 800 RPM as shown in FIG. 4). In this way, a jump in the motor speed at a certain duty cycle is achieved.

The above as well as other objects, features and advantages of the present invention will become more apparent from the description of the preferred embodiments.

1‧‧‧Motor speed control device

11‧‧‧Voltage generation module

12‧‧‧PWM signal conversion module

13‧‧‧Follower

14‧‧‧Control signal output terminal

2‧‧‧Motor control circuit

3‧‧‧Motor

AR1‧‧‧First Comparator

AR2‧‧‧Second comparator

C1‧‧‧first capacitor

C2‧‧‧second capacitor

D1‧‧‧first diode

D2‧‧‧second diode

N1, N2‧‧‧ joints

OUT1P, OUT2P, OUT1N, OUT2N‧‧‧ pins

Q1‧‧‧First switching element

Q2‧‧‧Second switching element

R1‧‧‧first resistance

R2‧‧‧second resistance

R3‧‧‧ third resistor

R4‧‧‧fourth resistor

R5‧‧‧ fifth resistor

R6‧‧‧ sixth resistor

R7‧‧‧ seventh resistor

R8‧‧‧ eighth resistor

R9‧‧‧ ninth resistor

S1‧‧‧First series resistor string

S2‧‧‧Second series resistor string

S3‧‧‧ third series resistor string

Vc‧‧‧ voltage signal

ZD1‧‧‧Zener diode

Figures 1 through 4 show four motor speed control curves.

Fig. 5 is a schematic view showing the structure of an embodiment of the motor rotation speed control device of the present application.

Fig. 6 is a schematic view showing the structure of another embodiment of the motor rotation speed control device of the present application.

Fig. 7 is a schematic view showing the structure of a motor rotation speed control system of the present application.

Fig. 8 schematically shows a partial schematic view of the drive IC LB11967.

FIG. 9 shows the correspondence between the duty ratio of the PWM signal, the voltage signal Vc converted by the PWM signal conversion module based on the PWM signal, the OSC signal input to the CPWM pin of the driver IC, the motor voltage, and the motor rotation speed.

Fig. 10 schematically shows a motor rotation speed control curve in which a hysteresis phenomenon exists.

Fig. 11 schematically shows a motor speed control curve in which hysteresis is eliminated.

Fig. 12 is a flow chart schematically showing an embodiment of the motor rotation speed control method of the present application.

Fig. 5 is a schematic view showing the structure of an embodiment of the motor rotation speed control device of the present application. The motor rotation speed control device 1 includes a reference voltage generation module 11, a PWM signal conversion module 12, a first comparator AR1, a first switching element Q1, a follower 13, and a control signal output terminal 14.

The reference voltage generating module 11 is configured to generate a reference voltage. In the embodiment of the present application, the reference voltage generating module 11 is not limited as long as it is a module capable of generating a reference voltage. For example, a reference voltage can be generated by a voltage dividing circuit.

The PWM signal conversion module 12 is configured to convert the PWM signal into a voltage signal, the voltage signal corresponding to the duty cycle of the PWM signal, and specifically, the voltage signal may be inversely proportional to the duty cycle of the PWM signal. The specific configuration of the PWM signal conversion module 12 is also not limited as long as it is a module capable of converting a PWM signal into a voltage signal corresponding to the duty ratio.

The positive terminal of the first comparator AR1 is connected to the reference voltage generating module 11, and the negative terminal is connected to the PWM signal conversion module 12, and is used when the voltage of the voltage signal converted into the PWM signal is less than or equal to the reference voltage, that is, the PWM signal When the null ratio is greater than or equal to the duty ratio corresponding to the reference voltage (assuming the duty ratio corresponding to the reference voltage is A%, 0% ≦ A% ≦ 100%), the first level is output, and the voltage converted to the PWM signal is When the voltage of the signal is greater than the reference voltage, that is, the duty ratio of the PWM signal is less than the duty ratio (A%) corresponding to the reference voltage, the second level is output.

The control end of the first switching element Q1 is connected to the output end of the first comparator AR1, and the first end of the first switching element Q1 inputs a first signal for receiving the second output at the output end of the first comparator AR1. The level is turned on to connect the first end and the second end of the first switching element Q1 and is turned off when receiving the first level outputted by the output of the first comparator AR1. The first switching element Q1 may be a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) or a Bipolar Junction Transistor (BJT).

The input of the follower 13 is connected to the PWM signal conversion module 12. The follower 13 is capable of isolating the input and output, that is, isolating the voltage signal output from the PWM signal conversion module 12 from the signal input to the control signal output terminal 14.

The control signal output terminal 14 is respectively connected to the second end of the first switching element Q1 and the output of the follower 13 for receiving the first signal received through the second end of the first switching element Q1 or through the follower 13. The voltage signal converted into the PWM signal is output to a motor control circuit (see FIG. 7).

The motor control circuit is operative to generate a motor speed control signal based on a signal received from the control signal output terminal 14 to control the rotational speed of the motor. Specifically, when the first switching element Q1 is turned on, since the first end of the first switching element Q1 inputs the first signal, the motor control circuit inputs the first signal, and the first signal causes the motor control circuit to control the motor speed to be 0 or a determined speed; when the first switching element Q1 is turned off, the voltage signal converted into the PWM signal is input to the motor control circuit through the follower 13 so that the motor control circuit controls the motor rotation speed to be determined by the duty ratio of the PWM signal. Specifically, the motor speed may increase as the duty ratio of the PWM signal increases, that is, as the voltage signal converted by the PWM signal decreases.

The motor control circuit can be a driver IC, and the value of the first signal can be determined by the actual demand of the driver IC. For example, if the drive IC can input a high level to control the rotational speed of the motor to be 0 or a determined speed (eg, low speed), the first signal can be a high level signal, such as a power supply voltage (VCC) signal.

In an embodiment of the present application, the first level and the second level may be set according to the type of the first switching element Q1. For example, if the first switching element Q1 is an N-type MOSFET, the first level may be a low level that causes the N-type MOSFET to be turned off, and the second level may be a high level, the low level making The N-type MOSFET is turned on. If the first switching element Q1 is a P-type MOSFET, the first level may be a high level, the high level causes the P-type MOSFET to be turned off, and the second level may be a low level, the low level making the P The MOSFET is turned on.

In the motor rotation speed control device 1 as described above, it can be seen that when the voltage of the voltage signal converted into the PWM signal is less than or equal to the reference voltage, that is, the duty ratio of the PWM signal is greater than or equal to the duty corresponding to the reference voltage. When the ratio is A%, the first level outputted by the first comparator AR1 causes the first switching element Q1 to be turned off, thereby inputting a voltage signal into which the PWM signal is converted to the motor control circuit, so that the motor control circuit controls the motor speed with the PWM signal The duty ratio of the PWM signal changes; when the voltage of the voltage signal converted by the PWM signal is greater than the reference voltage, that is, the duty ratio of the PWM signal is less than the duty ratio A% corresponding to the reference voltage, the first comparator AR1 outputs The second level causes the first switching element Q1 to be turned on, thereby inputting the first signal to the motor control circuit such that the motor control circuit controls the motor speed to be 0 or a determined speed (eg, approximately 800 RPM as shown in FIG. 3) . In this way, a jump in the motor speed at a certain duty cycle A% is achieved.

The control curve shown in Figures 3 and 4 has three segments, the first segment is the rotational speed plateau region, the second segment is the rotational speed abrupt change zone, and the third segment is the rotational speed relaxation zone. By adopting the motor rotation speed control device provided by the embodiment of the present application, the three-stage rotation speed control curve as shown in FIG. 3 and FIG. 4 can be realized, and more flexible motor speed control is provided.

Fig. 6 is a schematic view showing the structure of another embodiment of the motor rotation speed control device of the present application. This embodiment gives a specific structure regarding each module in the motor speed control device.

In this embodiment, the follower 13 includes a second comparator AR2, a first resistor R1, a second resistor R2, and a third resistor R3.

The positive terminal of the second comparator AR2 is connected to the output of the PWM signal conversion module 12. The first end of the first resistor R1 is coupled to the negative terminal of the second comparator AR2. The first end of the second resistor R2 is connected to the output end of the second comparator AR2, and the second end of the second resistor R2 is connected to the second end of the first resistor R1. The first end of the third resistor R3 is connected to the second end of the second resistor R2, and the second end of the third resistor R3 is connected to the control signal output terminal 14.

The reference voltage generating module 11 includes a first diode D1, a fourth resistor R4, a Zener diode ZD1, a first capacitor C1, a first series resistor string S1, and a fifth resistor R5.

The anode of the first diode D1 inputs a VCC signal. The first end of the fourth resistor R4 is coupled to the cathode of the first diode. The cathode of the Zener diode ZD1 is connected to the second end of the fourth resistor R4, and the anode of the Zener diode ZD1 is grounded. Both ends of the first capacitor C1 are respectively connected to the cathode and the anode of the Zener diode ZD1. The first end of the first series resistor string S1 is connected to the cathode of the Zener diode ZD1. The first end of the fifth resistor R5 is connected to the second end of the first series resistor string S1, and the second end of the fifth resistor R5 is grounded. The common terminal N1 of the second end of the first series resistor string S1 and the first end of the fifth resistor R5 is connected to the positive terminal of the first comparator AR1.

In this embodiment, the Zener diode ZD1 is used to generate the reference voltage, which ensures a stable reference voltage. By inputting this stable reference voltage to the positive terminal of the first comparator, it is possible to eliminate the motor from being unable to jump at a set duty ratio due to voltage fluctuations, thereby achieving precise control.

In FIG. 6, the PWM signal conversion module 12 includes a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a second switching element Q2, a second diode D2, a second series resistor string S2, and a third series resistor string. S3, a second capacitor C2, and a ninth resistor R9.

The first end of the sixth resistor R6 is connected to the cathode of the Zener diode ZD1. The first end of the seventh resistor R7 is connected to the second end of the sixth resistor R6, and the second end of the seventh resistor R7 is grounded. The first end of the eighth resistor R8 is connected to the first end of the seventh resistor R7 and the second end of the sixth resistor R6, and the first end of the eighth resistor R8 receives the PWM signal. The control terminal of the second switching element Q2 is connected to the second terminal of the eighth resistor R8, and the second terminal of the second switching element Q2 is grounded. The anode of the second diode D2 is connected to the first end of the second switching element Q2. The first end of the second series resistor string S2 is coupled to the first end of the sixth resistor R6, the second end of the second series resistor string S2 and the anode of the second diode D2 and the first end of the second switching element Q2 connection. The first end of the third series resistor string S3 is connected to the first end of the sixth resistor R6, and the second end of the third series resistor string S3 is connected to the cathode of the second diode D2. The first end of the second capacitor C2 is connected to the second end of the third series resistor string S3, and the second end of the second capacitor C2 is grounded. The first end of the ninth resistor R9 is connected to the cathode of the second diode D2, and the second end of the ninth resistor R9 is grounded. The second end of the third series resistor string S3, the first end of the second capacitor C2, the cathode of the second diode D2, and the common junction N2 of the first end of the ninth resistor R9 serve as outputs of the PWM signal conversion module 11. end.

It should be noted that the PWM signal conversion module 12, the reference voltage generation module 11, and the follower 13 in the embodiment of the present application are not limited to the structure shown in FIG. 6, and other configurations may be employed.

Fig. 7 is a schematic block diagram showing an embodiment of a motor speed control system of the present application, which includes a motor 3, a motor control circuit 2, and a motor speed control device 1. The motor 3 is connected to the motor control circuit 2, and the motor control circuit 2 controls the number of revolutions of the motor 3. The motor rotational speed control device 1 is connected to the motor control circuit 2, and the motor control circuit 2 controls the rotational speed of the motor 3 based on a signal output from the control signal output terminal 14 of the motor rotational speed control device 1.

The motor control circuit 2 can be a drive IC such as LB11967. Fig. 8 schematically shows a partial schematic view of LB11967. In the figure, the VTH pin (shown by the circle in the figure) is input to the signal output from the control signal output terminal 14 of the motor speed control device 1, and the CPWM pin (shown by the elliptical circle in the figure) is input to the OSC signal, which is the drive IC. An internal voltage signal, which is generally a sawtooth voltage signal obtained by charging and discharging a capacitor, and comparing the voltage signal with a voltage signal input to the VTH pin (for example, a voltage signal Vc converted according to the PWM signal). Thereby different motor drive voltage signals are obtained to achieve control of the motor. The motor control signal is the signal of the four pins OUT1P, OUT2P, OUT1N, and OUT2N in the figure.

FIG. 9 shows the duty ratio of the PWM signal, the voltage signal Vc converted by the PWM signal conversion module 12 based on the PWM signal, the OSC signal of the CPWM pin input of the driver IC, the motor voltage, and the motor rotation speed.

The principle of motor rotation speed control in the embodiment of the present application will be described below with reference to FIGS. 6 to 9.

In the embodiment shown in FIG. 6, the on and off of the first switching element Q1 are controlled by the output level of the first comparator AR1, and different control signals are obtained by turning on and off the first switching element Q1. This control signal is input to the motor speed control circuit 2, for example, to the VTH pin of the LB11967, thereby achieving a jump of the motor 3 at a certain duty ratio A%.

Specifically, referring to FIG. 9, the duty ratio of the PWM signal is inversely proportional to the voltage signal Vc converted by the PWM signal conversion module 12, that is, the voltage signal Vc converted by the PWM signal conversion module 12 increases with the duty ratio of the PWM signal. And decrease.

When the voltage of the voltage signal Vc converted into the PWM signal is greater than the reference voltage, that is, the duty ratio of the PWM signal is less than the duty ratio A% corresponding to the reference voltage, the first comparator AR1 outputs the second level (eg, low power) Flat), the first switching element Q1 (for example, the first switching element is a P-type MOSFET) is turned on. At this time, the first switching element Q1 supplies the VCC signal to the motor rotation speed control circuit 2, that is, the high level is supplied to the motor rotation speed control circuit 2, which controls the motor rotation speed to 0 (see FIG. 3) or a certain low speed. (For example, about 800 RPM in Figure 4).

When the voltage of the voltage signal converted into the PWM signal is less than or equal to the reference voltage, that is, the duty ratio of the PWM signal is greater than or equal to the duty ratio A% corresponding to the reference voltage, the first comparator AR1 outputs the first level ( For example, a high level), the first switching element Q1 is turned off. At this time, the voltage signal Vc converted from the PWM signal output from the follower 13 is supplied to the control pin of the motor rotation speed control circuit 2, the motor is started and the rotation speed is determined by the duty ratio of the PWM signal, specifically, the motor rotation speed can follow The duty cycle of the PWM signal increases as the duty ratio increases (see Figure 9).

Thus, when the duty ratio of the PWM signal reaches A%, the motor speed control device 1 can control the speed jump of the motor.

In the embodiment of the present application, the follower 13 is used to supply the voltage signal Vc converted by the PWM signal conversion module 12 to the control pin of the driving IC, thereby achieving isolation of the input and output, thereby eliminating hysteresis.

The following is to explain the hysteresis phenomenon. The so-called "hysteresis" refers to the phenomenon that the speed control curve when the duty cycle of the PWM signal goes up (ie, increases) does not coincide with the speed control curve when the duty cycle of the PWM signal goes down (ie, decreases), especially in the jump. The variable regions do not overlap, as shown by the portion enclosed by the elliptical circle in FIG.

The cause of hysteresis is that the input impedance of the driver IC is high, and the higher input impedance is input to the first comparator AR1, thereby affecting the operation of the first comparator AR1, resulting in the first comparator AR1 not being able to be in the PWM. The same output signal switching is achieved when the signal duty cycle is up and down. After the follower 13 of the present application is employed, since the follower has an isolation function, the input impedance of the driver IC can be prevented from being input to the first comparator AR1, thereby effectively eliminating hysteresis (see FIG. 11).

Fig. 12 is a flow chart schematically showing an embodiment of the motor rotation speed control method of the present application. The method includes:

S1: Converting the PWM signal into a voltage signal by using a PWM conversion module, and comparing the voltage of the converted PWM voltage signal with a reference voltage by the first comparator. If the voltage of the voltage signal converted into the PWM signal is greater than the reference voltage, step S2 is performed, and if the voltage of the voltage signal converted into the PWM signal is less than or equal to the reference voltage, step S3 is performed.

S2, outputting a second level through the first comparator, so that the first switching element is turned on to connect the first end and the second end of the first switching element, and send the first signal received by the first end to the motor control The circuit causes the motor control circuit to control the motor speed to be zero or a determined speed.

S3. The first level is outputted by the first comparator, so that the first switching element is turned off, and the voltage signal converted by the PWM signal conversion module is supplied to the motor control circuit by the follower, so that the motor speed is determined by the duty ratio of the PWM signal. .

For the specific process of the motor speed control method in the embodiment of the present application, reference may be made to the descriptions described above with reference to FIGS. 5-8, and details are not described herein again.

While the present application has been described with reference to a few exemplary embodiments, it is understood that the terms used are illustrative and exemplary and not restrictive. Since the present application can be embodied in a variety of forms without departing from the spirit or scope of the invention, it is to be understood that the embodiments are not limited to the details of the foregoing, but are construed broadly within the spirit and scope defined by the appended claims. Therefore, all changes and modifications that fall within the scope of the patent application or its equivalents should be covered by the accompanying claims.

11‧‧‧Voltage generation module

12‧‧‧PWM signal conversion module

13‧‧‧Follower

14‧‧‧Control signal output terminal

AR1‧‧‧First Comparator

Q1‧‧‧First switching element

Claims (1)

A motor speed control device includes:

a reference voltage generating module for generating a reference voltage;

a pulse width modulation (PWM) signal conversion module for converting the PWM signal into a voltage signal, the voltage signal corresponding to a duty cycle of the PWM signal;

a first comparator, the positive end of which is connected to the reference voltage generating module, and the negative end thereof is connected to the PWM signal conversion module, and is configured to output when the voltage of the voltage signal converted by the PWM signal is less than or equal to the reference voltage a level, when the voltage of the voltage signal converted by the PWM signal is greater than the reference voltage, outputting a second level;

a first switching element, the control end of which is connected to the output end of the first comparator, and the first end thereof inputs a first signal for conducting when receiving the second level outputted by the output end of the first comparator, Connecting the first end of the first switching element to the second end, and cutting off when receiving the first level outputted by the output end;

a follower whose input is connected to the PWM signal conversion module;

Control signal output terminals respectively connected to the second end of the first switching element and the output of the follower for receiving the first signal through the second end of the first switching element or through the follower The voltage signal converted by the received PWM signal is output to the motor control circuit;

Wherein, when the first switching element is turned on, the motor control circuit inputs the first signal, the first signal causes the motor control circuit to control the motor speed to be 0 or a determined speed; when the first switching element is turned off, The motor control circuit inputs a voltage signal converted by the PWM signal such that the motor speed is determined by a duty cycle of the PWM signal.

2. The motor speed control device according to claim 1, wherein the follower comprises:

a second comparator whose positive terminal is connected to an output end of the PWM signal conversion module,

a first resistor having a first end connected to a negative end of the second comparator;

a second resistor having a first end coupled to the output of the second comparator and a second end coupled to the second end of the first resistor;

The third resistor has a first end connected to the second end of the second resistor and a second end connected to the control signal output terminal.

3. The motor speed control device according to claim 1 or 2, wherein the reference voltage generating module comprises:

a first diode whose anode inputs the first signal;

a fourth resistor having a first end connected to a cathode of the first diode;

a Zener diode having a cathode connected to the second end of the fourth resistor and having an anode grounded;

a first capacitor, the two ends of which are respectively connected to the cathode and the anode of the Zener diode;

a first series resistor string having a first end coupled to a cathode of the Zener diode;

a fifth resistor having a first end connected to the second end of the first series resistor string and a second end grounded;

The common junction of the second end of the first series resistor string and the first end of the fifth resistor is connected to the positive terminal of the first comparator.

4. The motor speed control device according to claim 3, wherein the PWM signal conversion module comprises:

a sixth resistor having a first end connected to a cathode of the Zener diode;

a seventh resistor having a first end connected to the second end of the sixth resistor and a second end grounded;

An eighth resistor, the first end of which is coupled to the first end of the seventh resistor and the second end of the sixth resistor, and the first end thereof receives the PWM signal;

a second switching element having a control end connected to the second end of the eighth resistor and a second end grounded;

a second diode having an anode connected to the first end of the second switching element;

a second series resistor string having a first end connected to the first end of the sixth resistor and a second end connected to the anode of the second diode and the first end of the second switching element;

a third series resistor string having a first end connected to the first end of the sixth resistor and a second end connected to the cathode of the second diode;

a second capacitor having a first end connected to the second end of the third series resistor string and a second end grounded;

a ninth resistor having a first end connected to the cathode of the second diode and a second end grounded;

The common end of the second end of the third series resistor string, the first end of the second capacitor, the cathode of the second diode, and the first end of the ninth resistor is used as the PWM signal conversion module. Output.

5. A motor speed control method implemented by the motor conversion device according to claim 1, wherein:

Converting the PWM signal into a voltage signal by a pulse width modulation (PWM) signal conversion module, and comparing the voltage of the converted PWM voltage signal with a reference voltage through the first comparator;

If the voltage of the voltage signal converted by the PWM signal is greater than the reference voltage, outputting the second level through the first comparator, so that the first switching element is turned on to the first end and the second end of the first switching element End communication, transmitting the first signal received by the first end of the first switching element to the motor control circuit, such that the motor control circuit controls the motor speed to be 0 or a determined speed;

If the voltage of the voltage signal converted by the PWM signal is less than or equal to the reference voltage, the first level is outputted by the first comparator, so that the first switching element is turned off, and the voltage converted by the PWM signal conversion module is converted by the follower. The signal is provided to the motor control circuit such that the motor speed is determined by the duty cycle of the PWM signal.

6. A motor speed control system comprising:

motor;

a motor control circuit coupled to the motor for controlling the rotational speed of the motor;

a motor speed control device connected to the motor control circuit;

The motor speed control device includes:

a reference voltage generating module for generating a reference voltage;

a pulse width modulation (PWM) signal conversion module for converting the PWM signal into a voltage signal, the voltage signal corresponding to a duty cycle of the PWM signal;

a first comparator, the positive end of which is connected to the reference voltage generating module, and the negative end thereof is connected to the PWM signal conversion module, and is configured to output when the voltage of the voltage signal converted by the PWM signal is less than or equal to the reference voltage a level, when the voltage of the voltage signal converted by the PWM signal is greater than the reference voltage, outputting a second level;

a first switching element, the control end of which is connected to the output end of the first comparator, and the first end thereof inputs a first signal for conducting when receiving the second level outputted by the output end of the first comparator, Connecting the first end of the first switching element to the second end, and cutting off when receiving the first level outputted by the output end;

a follower whose input is connected to the PWM signal conversion module;

Control signal output terminals respectively connected to the second end of the first switching element and the output of the follower for receiving the first signal through the second end of the first switching element or through the follower The voltage signal converted by the received PWM signal is output to the motor control circuit;

Wherein, when the first switching element is turned on, the motor control circuit inputs the first signal, the first signal causes the motor control circuit to control the motor speed to be 0 or a determined speed; when the first switching element is turned off, The motor control circuit inputs a voltage signal converted by the PWM signal such that the motor speed is determined by a duty cycle of the PWM signal.

7. The motor speed control system of claim 6, wherein the follower comprises:

a second comparator whose positive terminal is connected to an output end of the PWM signal conversion module,

a first resistor having a first end connected to a negative end of the second comparator;

a second resistor having a first end coupled to the output of the second comparator and a second end coupled to the second end of the first resistor;

The third resistor has a first end connected to the second end of the second resistor and a second end connected to the control signal output terminal.

8. The motor speed control system according to claim 6 or 7, wherein the reference voltage generating module comprises:

a first diode whose anode inputs the first signal;

a fourth resistor having a first end connected to a cathode of the first diode;

a Zener diode having a cathode connected to the second end of the fourth resistor and having an anode grounded;

a first capacitor, the two ends of which are respectively connected to the cathode and the anode of the Zener diode;

a first series resistor string having a first end coupled to a cathode of the Zener diode;

a fifth resistor having a first end connected to the second end of the first series resistor string and a second end grounded;

The common junction of the second end of the first series resistor string and the first end of the fifth resistor is connected to the positive terminal of the first comparator.

9. The motor speed control system of claim 8, wherein the PWM signal conversion module comprises:

a sixth resistor having a first end connected to a cathode of the Zener diode;

a seventh resistor having a first end connected to the second end of the sixth resistor and a second end grounded;

An eighth resistor, the first end of which is coupled to the first end of the seventh resistor and the second end of the sixth resistor, and the first end thereof receives the PWM signal;

a second switching element having a control end connected to the second end of the eighth resistor and a second end grounded;

a second diode having an anode connected to the first end of the second switching element;

a second series resistor string having a first end connected to the first end of the sixth resistor and a second end connected to the anode of the second diode and the first end of the second switching element;

a third series resistor string having a first end connected to the first end of the sixth resistor and a second end connected to the cathode of the second diode;

a second capacitor having a first end connected to the second end of the third series resistor string and a second end grounded;

a ninth resistor having a first end connected to the cathode of the second diode and a second end grounded;

The common end of the second end of the third series resistor string, the first end of the second capacitor, the cathode of the second diode, and the first end of the ninth resistor is used as the PWM signal conversion module. Output.